1. Field of the Invention
The present invention relates to the use of raw materials containing kerogen (or other organic combustible constituents) for manufacture of Portland cement in a rotary kiln and suspension cyclone preheater system.
2. Description of the Prior Art
Heretofore use of kerogen containing raw materials posed difficulties for cement rotary kilns equipped with suspension cyclone preheaters. In this respect, combustion or organic combustible constituents in the lower cyclone stages brought about an imbalance in the maintenance of gas/material temperature in the preheater cyclones. Also there was a hazard of explosion in the cyclone preheater stages.
In copending application Ser. No. 310,771 for: METHOD AND APPARATUS FOR PREHEATING DRY RAW MEAL PRIOR TO THE INTRODUCTION OF THE MEAL INTO A SUSPENSION CYCLONE PREHEATER SYSTEM SUPPLYING A ROTARY KILN, filed contemporaneously herewith, the disclosure of which is incorporated herein by reference, there is disclosed a method and apparatus for preheat of raw meal prior to introduction of the raw meal into the first or later stage of a multistage cyclone preheater system. As will be described in greater detail hereafter, the present invention utilizes the teachings in the copending application Ser. No. 310,771 and adds to those teachings a method and apparatus for heating and burning the combustible kerogen constituents. This, as described hereinafter, in greater detail, is achieved by preheating the kerogen contained in the raw meal feed or the kerogen in added oil shale, etc. and bringing about combustion of the organic combustible kerogen constituent prior to entry of the feed and/or kerogen containing component into the preheater system. As described in the copending application serial no. additional oil, gas or pulverized coal is used as required in a separate combustion chamber to attain the desired raw meal preheat temperature. As taught by the present invention the kerogen constituent of the raw material/oil shale contributes part or all of the heat required.
It has heretofore been proposed to make Portland cement from oil shale and methods and apparatus heretofore proposed for making cement from oil shale are disclosed in the following U.S. Patents: